This invention relates to a novel solid catalyst component to be employed with a cocatalyst for use in the polymerization of olefins to polyolefins such as polyethylene, polypropylene and the like, or copolymers such as ethylene copolymers with other alpha-olefins and diolefins, which catalyst component shows unusually high activity, excellent hydrogen response for the control of polymer molecular weight and good comonomer response for the production of copolymers. The polymer product obtained has a good balance of polymer properties, for example, the catalyst system obtains a polymer with a broad molecular weight distribution and an improved balance in polymer product machine direction tear strength and transverse direction tear strength. As a result, the blown film produced from the polymer product manifests an overall higher strength. The invention also relates to polymerization catalyst systems comprising said component and polymerization processes employing such catalyst systems.
The catalyst component comprises a solid reaction product obtained by sequentially contacting a solid, particulate, porous support material such as, for example, silica, alumina, magnesia or mixtures thereof, for example, silica-alumina, with a dihydrocarbyl magnesium compound, optionally an oxygen containing organic compound, a vanadium compound and a Group IIIa metal halide or hydrocarbyl halide. The catalyst component, which when used with an aluminum alkyl cocatalyst, provides the catalyst system of this invention which can be usefully employed for the polymerization of olefins.
The catalyst system can be employed in slurry, single-phase melt, solution and gas-phase polymerization processes and is particularly effective for the production of linear polyethylenes such as high-density polyethylene and linear low density polyethylene (LLDPE).
It is known that catalysts of the type generally described as Ziegler-type catalysts are useful for the polymerization of olefins under moderate conditions of temperature and pressure. It is also well known that the properties of polymer product obtained by polymerizing olefins in the presence of Ziegler-type catalysts vary greatly as a function of the monomers of choice, catalyst components, catalyst modifiers and a variety of other conditions which affect the catalytic polymerization process.
For the production of high strength film, it is desirable that polymer product have a high molecular weight. However, high molecular weight resins such as polyethylene, which generally are of a narrow molecular weight distribution are difficultly processable.
It is therefore desirable to provide polyolefin resins having a high molecular weight so as to obtain high strength films therefrom coupled with a broad molecular weight distribution so as to provide an easily processable resin. It is furthermore highly desirable that the resin be produced by a commercially feasible and economical process which obtains polymer product having a good balance of properties.
U.S. Pat. No. 4,434,242 of Roling et al, issued Feb. 28, 1984, teaches a polymerization process for preparing injection molded resins by polymerizing ethylene in the presence of a vanadium based catalyst. However, as taught in the patent, the process provides resins having a narrow molecular weight distribution suitable for injection molded resins rather than blow molded resins.
In European Patent Application No. 55589, Asahi teaches treating an oxide support with an organomagnesium composition, a chlorosilane and then treating with a titanium or vanadium compound that has at least one halogenated atom. As demonstrated in Example 7, the resin obtains a relatively narrow molecular weight distribution which is statistically in the same range as the resins produced in the presence of titanium based catalysts.
Soviet No. 422,192 treats a silica support with an organoaluminum compound and a chlorinating agent and thereafter adds TiCl.sub.4 to the material so as to obtain an active catalyst. The production of polyethylene having a high molecular weight and coupled with a broad molecular weight distribution is not disclosed.
U.S. Pat. No. 4,385,161 of Caunt et al describes a catalyst component obtained by contacting an inert particulate material with an organic compound, a halogen-containing compound, including boron trichloride and a transition metal compound such as VOCl.sub.3. The active ingredients can be added to the inert particulate material all together in a single stage or preferably by adding the various components in sequence with the transition metal compound being added in the last stage.
The above patents do not suggest how its processes might be modified to result in the rapid production of polymers having a broad molecular weight distribution preferably coupled with a high molecular weight so as to provide resins suitable for the production of high-strength film polymers having a high MI together with a relatively high MIR.
Furthermore, the patents do not disclose catalyst systems which show excellent responsiveness to hydrogen during the polymerization reaction for the control of molecular weight, do not disclose or evidence the excellent comonomer response so as to produce ethylene copolymers and particularly LLDPE, and particularly do not disclose highly active catalyst systems which will obtain polymer at a very high rate of production.
In accordance with this invention catalyst combinations have been found which have extremely high catalytic activities, good comonomer incorporation, excellent hydrogen responsiveness for the control of molecular weight and obtain polymer product manifesting a broad molecular weight distribution with greatly improved film properties. The resins exhibit excellent melt strength with a surprising decrease in power consumption, hence an increase in extrusion rates, as well as excellent MD tear stength.
The new catalyst systems and catalyst component of this invention are obtained by contacting a dihydrocarbyl magnesium compound, a vanadium metal compound and a Group IIIa metal halide or hydrocarbyl halide in the presence of an inert particulate support. The catalyst system employing the vanadium based catalyst component is advantageously employed in a gas phase ethylene polymerization process since there is a significant decrease in reactor fouling as generally compared with prior art ethylene gas phase polymerization processes thereby resulting in less frequent reactor shut downs for cleaning.